If there's no top-cover to the lock mechanism, it's sure to come off. To be fair, the Witem brand has good blades naman... it's just the lack of the top cover that Bosch has lets the plastic latch flex too much, which causes eventual breakage, especially if the wiper is 20" long.

I think that in the case of frameless wipers, it's best not to go cheap. Get the Bosch ones... they're more than worth the extra money.